If you did install kdelibs, then the Qt version that is picked up by
this configure is not the same version you used to compile kdelibs.
The Qt Plugin installed by kdelibs is *ONLY* loadable if it is the
_same Qt version_, compiled with the _same compiler_ and the same Qt
configuration settings.

!!! Please attach the following file when filing a report to bugs.gentoo.org:
!!! /var/tmp/portage/kde-base/kdeaddons-3.5.7/work/kdeaddons-3.5.7/config.log

!!! econf failed
!!! If you need support, post the topmost build error, and the call stack if relevant.
!!! A complete build log is located at '/var/tmp/portage/kde-base/kdeaddons-3.5.7/temp/build.log'.